Hypothesis: The purpose of this study is to define how KC control T-cell mediated immunity in the skin. We will utilize both human and mouse models of the common skin condition, allergic contact dermatitis (ACD). We selected this skin condition because it is a common skin disease in Veterans. We hypothesize that Keratinocytes (KC) are tolerigenic Antigen presenting cells for Natural killer (NK)T-cells. KC-NKT-cell interactions via CD1d plays an important role in maintaining peripheral tolerance by inducing NKT clonal anergy. We will test our central hypothesis CD1d on KC may tolerize epidermotropic NKT, potentially dampening contact dermatitis. We will study KC-NKT-cell interactions, and how they affect cell mediated immunity in the skin, using mouse models as well as direct studies of human KC and NKT-cells. Specific Objectives: There are three specific objectives: 1) To study the effects of KC- NKT-cell interactions in vitro and whether this tolerizes NKT-cells. 2) To define the role of anergic iNKT-cells in the afferent and efferent phases of murine ACD. 3) To determine the effects of the loss of CD1d by epidermal KC on ACD (loss of tolerance). Relevance to the VA: Contact dermatitis a very common inflammatory skin diseases in the industrialized world. It is a major health concern for patients and has a major impact on the economy. Contact dermatitis is a significant problem for veterans as well, representing a common cause for visits to Dermatology clinics in veterans. Subject Populations: KC and NKT-cells will be obtained from healthy controls for in vitro studies. An animal model system will be used to ACD in mice engrafted with skin from CD1d gene knockout mice. This in vivo model will allow us to confirm the role of KC derived CD1d, and will extend our in vitro studies on the role of CD1d in controlling innate immunity in vivo. Procedures: Tissue culture of KC, NKT-cells, monocytes, cell proliferation assays, flow cytometry, ELISA, qPCR, in vivo studies with gene targeted mice will be utilized to address the questions that are the central focus of this proposal: How KC CD1d controls NKT-cell responses, and this controls the course of ACD. Significance of findings to the VA: Dermatitis a common skin disease in Veterans as it is in the general population. Veterans returning from the Middle East Conflicts will experience health problems, including diseases of the immune system that will affect the skin, such as contact dermatitis. The proposed studies are of a fundamental nature that will further the understanding of the interface between innate immunity (NKT-cells), and tissues that interface with the environment (in this proposal epithelial surfaces in the skin), and are relevant to allergic diseases in other organs such as asthma. The proposed immunological study will utilize ACD as a model to dissect out patho-mechanisms of this disease. These studies will be of great utility in understanding this common skin disease, and will be applied to allergic health problems in Veterans returning from the Middle East Conflicts.